I just noticed this problem myself. I created my first nether portal at coordinates 948, 71, -218. I went through, found that the portal spawned right over some lava, decided to leave and try to build somewhere else, and when I exited the nether a new portal was created at coordinates 815, 63, -83. I tried deactivating my portal and trying again with a copy of my world and the same thing happened.
Grace Thompson
I just noticed this problem myself. I created my first nether portal at coordinates 948, 71, -218. I went through, found that the portal spawned right over some lava, decided to leave and try to build somewhere else, and when I exited the nether a new portal was created at coordinates 815, 63, -83. I tried deactivating my portal and trying again with a copy of my world and the same thing happened.